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Female bias in autoimmune disease can be profound, with nine females developing lupus for every male affected, and nearly twice that ratio seen in Sjögren disease.
For years, researchers have worked to determine the reasons for sex-linked differences in immune response and autoimmunity, with environmental factors, sex hormones, and X-chromosome inactivation — the process by which a second X chromosome is silenced — all seen as having roles.
More recently, different groups of researchers have homed in on a long noncoding RNA fragment called X-inactive specific transcript, or Xist, as a potential driver of sex bias in autoimmune disease. Xist, which occurs in female mammals, has been known since the 1990s as the master regulator of X-chromosome inactivation, the process by which the second X chromosome is silenced, averting a fatal double dose of X-linked genes.
The inactivation process, which scientists liken to wrapping the extra X with a fluffy cloud of proteins, occurs early in embryonic development. After its initial work silencing the X, Xist is produced throughout the female’s life, allowing X inactivation to be maintained.
But is it possible that Xist, and the many dozens of proteins it recruits to keep that extra X chromosome silent, can also provoke autoimmunity? This is the question that several teams of researchers have been grappling with, resulting in provocative findings and opening exciting new avenues of discovery.
Xist Protein Complexes Make Male Mice Vulnerable to Lupus
In February, researchers Howard Chang, MD, PhD, and Diana Dou, PhD, of Stanford University in Stanford, California, made worldwide news when they published results from an experiment using male mice genetically engineered to carry a non-silencing form of Xist on one of their chromosomes.
Xist acts like a scaffold, recruiting multiple protein complexes to help it do its job. Dr. Dou explained in an interview that her team has been eyeing suspiciously for years the dozens of proteins Xist recruits in the process of X-chromosome inactivation, many of which are known autoantigens.
When the mice were injected with pristane, a chemical that induces lupus-like autoimmunity in mice, the Xist-producing males developed symptoms at a rate similar to that of females, while wild-type male mice did not.
By using a male model, the scientists could determine whether Xist could cause an increased vulnerability for autoimmunity absent the influence of female hormones and development. “Everything else about the animal is male,” Dr. Dou commented. “You just add the formation of the Xist ribonucleoprotein particles — Xist RNA plus the associating proteins — to male cells that would not ordinarily have these particles. Is just having the particles present in these animals sufficient to increase their autoimmunity? This is what our paper showed: That just having expression of Xist, the presence of these Xist [ribonucleoproteins], is enough in permissive genetic backgrounds to invoke higher incidence and severity of autoimmune disease development in our pristane-induced lupus model.”
The Stanford group sees the Xist protein complex, which they have studied extensively, as a key to understanding how Xist might provoke autoimmunity. Nonetheless, Dr. Dou said, “It’s important to note that there are other contributing factors, which is why not all females develop autoimmunity, and we had very different results in our autoimmune-resistant mouse strain compared to the more autoimmune-prone strain. Xist is a factor, but many factors are required to subvert the checkpoints in immune balance and allow the progression to full-blown autoimmunity.”
Faulty X Inactivation and Gene Escape
The understanding that Xist might be implicated in autoimmune disease — and explain some of its female bias — is not new.
About a decade ago, Montserrat Anguera, PhD, a biologist at the University of Pennsylvania, Philadelphia, began looking at the relationship of X-chromosome inactivation, which by definition involves Xist, and lupus.
Dr. Anguera hypothesized that imperfect X inactivation allowed for greater escape of genes associated with immunity and autoimmunity. Studying patients with lupus, Dr. Anguera found that the silencing process was abnormal, allowing more of these genes to escape the silenced X — including toll-like receptor 7 (TLR-7) and other genes implicated in the pathogenesis of lupus.
“If you get increased expression of certain genes from the [silenced] X, like TLR-7, it can result in autoimmune disease,” Dr. Anguera said. “So what we think is that in the lupus patients, because the silencing is impacted, you’re going to have more expression happening from the inactive X. And then in conjunction with the active X, that’s going to throw off the dosage [of autoimmunity-linked genes]. You’re changing the dosage of genes, and that’s what’s critical.”
Even among patients with lupus whose symptoms are well controlled with medication, “if you look at their T cells and B cells, they still have messed up X inactivation,” Dr. Anguera said. “The Xist RNA that’s supposed to be tethered to the inactive X in a fluffy cloud is not localized, and instead is dispersed all over the nucleus.”
Dr. Anguera pointed out that autoimmune diseases are complex and can result from a combination of factors. “You also have a host of hormonal and environmental contributors, such as previous viral infections,” she said. And of course men can also develop lupus, meaning that the X chromosome cannot explain everything.
Dr. Anguera said that, while the findings by the Stanford scientists do not explain the full pathogenesis of lupus and related diseases, they still support a strong role for Xist in sex-biased autoimmune diseases. “It’s sort of another take on it,” she said.
Is It the Proteins, the RNA, or Both?
The Stanford team points to the proteins recruited by Xist in the process of X-chromosome inactivation as the likely trigger of autoimmunity. However, a group of researchers at Johns Hopkins University in Baltimore, Maryland, made the case in a 2022 paper that Xist RNA itself was dangerous. They found that numerous short RNA sequences within the Xist molecule serve as ligands for TLR-7. And TLR-7 ligation causes plasmacytoid dendritic cells to overproduce type 1 interferon, a classic hallmark of lupus.
“Within rheumatology, the diseases that tend to be most female biased are the ones that are antibody positive and have this presence of upregulated interferon,” explained Brendan Antiochos, MD. “Lupus is an example of that. Sjögren’s syndrome is another. So there’s always been this quest to want to understand the mechanisms that explain why women would have more autoimmunity. And are there specific pathways which could contribute? One of the key pathways that’s been shown in humans and in mice to be important in lupus is toll-like receptor signaling.” Most convincingly, one recent study showed that people who have a gain-of-function mutation in their TLR-7 gene get a spontaneous form of lupus.
These findings led Erika Darrah, PhD, and her colleague Dr. Antiochos to begin looking more deeply into which RNAs could be triggering this signaling pathway. “We started to think: Well, there is this sex bias. Could it be that women have unique RNAs that could potentially act as triggers for TLR-7 signaling?” Dr. Darrah said.
Dr. Darrah and Dr. Antiochos looked at publicly available genetic data to identify sex-biased sources of self-RNA containing TLR-7 ligands. Xist, they found, was chock full of them. “Every time we analyzed that data, no matter what filter we applied, Xist kept popping out over and over again as the most highly female skewed RNA, the RNA most likely to contain these TLR-7 binding motifs,” Dr. Darrah said. “We started to formulate the hypothesis that Xist was actually promoting responses that were dangerous and pathogenic in lupus.”
That finding led the team to conduct in-vitro experiments that showed different fragments of Xist can activate TLR-7, resulting in higher interferon production. Finally, they looked at blood and kidney cells from women with lupus and found that higher Xist expression correlated with more interferon production, and higher disease activity. “The more Xist, the sicker people were,” Dr. Darrah said.
Xist’s Other Functions
Xist was first studied in the 1990s, and most research has centered on its primary role in X-chromosome inactivation. A research group led by Kathrin Plath, PhD, at the University of California, Los Angeles, has been occupied for years with untangling exactly how Xist does what it does. “It’s a very clever RNA, right? It can silence the whole chromosome,” Dr. Plath said in an interview.
In 2021, Dr. Plath and her colleagues established in detail how Xist executes silencing, setting down pairs of molecules in specific spots along the chromosome and building huge protein clouds around them. “We worked on learning where Xist binds and what proteins it binds, drilling down to understand how these proteins and the RNA are coming together.”
Dr. Plath has long suspected that Xist has other functions besides X inactivation, and she and her colleagues are starting to identify them. Early this year they published the surprising finding that Xist can regulate gene expression in autosomes, or non–sex-linked chromosomes, “which it might well also do in cancer cells and lymphocytes,” Dr. Plath said. “And now there is this new evidence of an autoimmune function,” she said. “It’s a super exciting time.”
The different hypotheses surrounding Xist’s role in sex-biased autoimmunity aren’t mutually exclusive, Dr. Plath said. “There’s a tremendous enrichment of proteins occurring” during X inactivation, she said, supporting the Stanford team’s hypothesis that proteins are triggering autoimmunity. As for the Johns Hopkins researchers’ understanding that Xist RNA itself is the trigger, “I’m totally open to that,” she said. “Why can’t it be an autoantigen?”
The other model in the field, Dr. Plath noted, is the one proposed by Dr. Anguera — “that there’s [gene] escape from X-inactivation — that females have more escape expression, and that Xist is more dispersed in the lymphocytes [of patients with lupus]. In fact, Xist becoming a little dispersed might make it a better antigen. So I do think everything is possible.”
The plethora of new findings related to autoimmunity has caused Dr. Plath to consider redirecting her lab’s focus toward more translational work, “because we are obviously good at studying Xist.” Among the mysteries Dr. Plath would like to solve is how some genes manage to escape the Xist cloud.
What is needed, she said, is collaboration. “Everyone will come up with different ideas. So I think it’s good to have more people look at things together. Then the field will achieve a breakthrough treatment.”
Female bias in autoimmune disease can be profound, with nine females developing lupus for every male affected, and nearly twice that ratio seen in Sjögren disease.
For years, researchers have worked to determine the reasons for sex-linked differences in immune response and autoimmunity, with environmental factors, sex hormones, and X-chromosome inactivation — the process by which a second X chromosome is silenced — all seen as having roles.
More recently, different groups of researchers have homed in on a long noncoding RNA fragment called X-inactive specific transcript, or Xist, as a potential driver of sex bias in autoimmune disease. Xist, which occurs in female mammals, has been known since the 1990s as the master regulator of X-chromosome inactivation, the process by which the second X chromosome is silenced, averting a fatal double dose of X-linked genes.
The inactivation process, which scientists liken to wrapping the extra X with a fluffy cloud of proteins, occurs early in embryonic development. After its initial work silencing the X, Xist is produced throughout the female’s life, allowing X inactivation to be maintained.
But is it possible that Xist, and the many dozens of proteins it recruits to keep that extra X chromosome silent, can also provoke autoimmunity? This is the question that several teams of researchers have been grappling with, resulting in provocative findings and opening exciting new avenues of discovery.
Xist Protein Complexes Make Male Mice Vulnerable to Lupus
In February, researchers Howard Chang, MD, PhD, and Diana Dou, PhD, of Stanford University in Stanford, California, made worldwide news when they published results from an experiment using male mice genetically engineered to carry a non-silencing form of Xist on one of their chromosomes.
Xist acts like a scaffold, recruiting multiple protein complexes to help it do its job. Dr. Dou explained in an interview that her team has been eyeing suspiciously for years the dozens of proteins Xist recruits in the process of X-chromosome inactivation, many of which are known autoantigens.
When the mice were injected with pristane, a chemical that induces lupus-like autoimmunity in mice, the Xist-producing males developed symptoms at a rate similar to that of females, while wild-type male mice did not.
By using a male model, the scientists could determine whether Xist could cause an increased vulnerability for autoimmunity absent the influence of female hormones and development. “Everything else about the animal is male,” Dr. Dou commented. “You just add the formation of the Xist ribonucleoprotein particles — Xist RNA plus the associating proteins — to male cells that would not ordinarily have these particles. Is just having the particles present in these animals sufficient to increase their autoimmunity? This is what our paper showed: That just having expression of Xist, the presence of these Xist [ribonucleoproteins], is enough in permissive genetic backgrounds to invoke higher incidence and severity of autoimmune disease development in our pristane-induced lupus model.”
The Stanford group sees the Xist protein complex, which they have studied extensively, as a key to understanding how Xist might provoke autoimmunity. Nonetheless, Dr. Dou said, “It’s important to note that there are other contributing factors, which is why not all females develop autoimmunity, and we had very different results in our autoimmune-resistant mouse strain compared to the more autoimmune-prone strain. Xist is a factor, but many factors are required to subvert the checkpoints in immune balance and allow the progression to full-blown autoimmunity.”
Faulty X Inactivation and Gene Escape
The understanding that Xist might be implicated in autoimmune disease — and explain some of its female bias — is not new.
About a decade ago, Montserrat Anguera, PhD, a biologist at the University of Pennsylvania, Philadelphia, began looking at the relationship of X-chromosome inactivation, which by definition involves Xist, and lupus.
Dr. Anguera hypothesized that imperfect X inactivation allowed for greater escape of genes associated with immunity and autoimmunity. Studying patients with lupus, Dr. Anguera found that the silencing process was abnormal, allowing more of these genes to escape the silenced X — including toll-like receptor 7 (TLR-7) and other genes implicated in the pathogenesis of lupus.
“If you get increased expression of certain genes from the [silenced] X, like TLR-7, it can result in autoimmune disease,” Dr. Anguera said. “So what we think is that in the lupus patients, because the silencing is impacted, you’re going to have more expression happening from the inactive X. And then in conjunction with the active X, that’s going to throw off the dosage [of autoimmunity-linked genes]. You’re changing the dosage of genes, and that’s what’s critical.”
Even among patients with lupus whose symptoms are well controlled with medication, “if you look at their T cells and B cells, they still have messed up X inactivation,” Dr. Anguera said. “The Xist RNA that’s supposed to be tethered to the inactive X in a fluffy cloud is not localized, and instead is dispersed all over the nucleus.”
Dr. Anguera pointed out that autoimmune diseases are complex and can result from a combination of factors. “You also have a host of hormonal and environmental contributors, such as previous viral infections,” she said. And of course men can also develop lupus, meaning that the X chromosome cannot explain everything.
Dr. Anguera said that, while the findings by the Stanford scientists do not explain the full pathogenesis of lupus and related diseases, they still support a strong role for Xist in sex-biased autoimmune diseases. “It’s sort of another take on it,” she said.
Is It the Proteins, the RNA, or Both?
The Stanford team points to the proteins recruited by Xist in the process of X-chromosome inactivation as the likely trigger of autoimmunity. However, a group of researchers at Johns Hopkins University in Baltimore, Maryland, made the case in a 2022 paper that Xist RNA itself was dangerous. They found that numerous short RNA sequences within the Xist molecule serve as ligands for TLR-7. And TLR-7 ligation causes plasmacytoid dendritic cells to overproduce type 1 interferon, a classic hallmark of lupus.
“Within rheumatology, the diseases that tend to be most female biased are the ones that are antibody positive and have this presence of upregulated interferon,” explained Brendan Antiochos, MD. “Lupus is an example of that. Sjögren’s syndrome is another. So there’s always been this quest to want to understand the mechanisms that explain why women would have more autoimmunity. And are there specific pathways which could contribute? One of the key pathways that’s been shown in humans and in mice to be important in lupus is toll-like receptor signaling.” Most convincingly, one recent study showed that people who have a gain-of-function mutation in their TLR-7 gene get a spontaneous form of lupus.
These findings led Erika Darrah, PhD, and her colleague Dr. Antiochos to begin looking more deeply into which RNAs could be triggering this signaling pathway. “We started to think: Well, there is this sex bias. Could it be that women have unique RNAs that could potentially act as triggers for TLR-7 signaling?” Dr. Darrah said.
Dr. Darrah and Dr. Antiochos looked at publicly available genetic data to identify sex-biased sources of self-RNA containing TLR-7 ligands. Xist, they found, was chock full of them. “Every time we analyzed that data, no matter what filter we applied, Xist kept popping out over and over again as the most highly female skewed RNA, the RNA most likely to contain these TLR-7 binding motifs,” Dr. Darrah said. “We started to formulate the hypothesis that Xist was actually promoting responses that were dangerous and pathogenic in lupus.”
That finding led the team to conduct in-vitro experiments that showed different fragments of Xist can activate TLR-7, resulting in higher interferon production. Finally, they looked at blood and kidney cells from women with lupus and found that higher Xist expression correlated with more interferon production, and higher disease activity. “The more Xist, the sicker people were,” Dr. Darrah said.
Xist’s Other Functions
Xist was first studied in the 1990s, and most research has centered on its primary role in X-chromosome inactivation. A research group led by Kathrin Plath, PhD, at the University of California, Los Angeles, has been occupied for years with untangling exactly how Xist does what it does. “It’s a very clever RNA, right? It can silence the whole chromosome,” Dr. Plath said in an interview.
In 2021, Dr. Plath and her colleagues established in detail how Xist executes silencing, setting down pairs of molecules in specific spots along the chromosome and building huge protein clouds around them. “We worked on learning where Xist binds and what proteins it binds, drilling down to understand how these proteins and the RNA are coming together.”
Dr. Plath has long suspected that Xist has other functions besides X inactivation, and she and her colleagues are starting to identify them. Early this year they published the surprising finding that Xist can regulate gene expression in autosomes, or non–sex-linked chromosomes, “which it might well also do in cancer cells and lymphocytes,” Dr. Plath said. “And now there is this new evidence of an autoimmune function,” she said. “It’s a super exciting time.”
The different hypotheses surrounding Xist’s role in sex-biased autoimmunity aren’t mutually exclusive, Dr. Plath said. “There’s a tremendous enrichment of proteins occurring” during X inactivation, she said, supporting the Stanford team’s hypothesis that proteins are triggering autoimmunity. As for the Johns Hopkins researchers’ understanding that Xist RNA itself is the trigger, “I’m totally open to that,” she said. “Why can’t it be an autoantigen?”
The other model in the field, Dr. Plath noted, is the one proposed by Dr. Anguera — “that there’s [gene] escape from X-inactivation — that females have more escape expression, and that Xist is more dispersed in the lymphocytes [of patients with lupus]. In fact, Xist becoming a little dispersed might make it a better antigen. So I do think everything is possible.”
The plethora of new findings related to autoimmunity has caused Dr. Plath to consider redirecting her lab’s focus toward more translational work, “because we are obviously good at studying Xist.” Among the mysteries Dr. Plath would like to solve is how some genes manage to escape the Xist cloud.
What is needed, she said, is collaboration. “Everyone will come up with different ideas. So I think it’s good to have more people look at things together. Then the field will achieve a breakthrough treatment.”
Female bias in autoimmune disease can be profound, with nine females developing lupus for every male affected, and nearly twice that ratio seen in Sjögren disease.
For years, researchers have worked to determine the reasons for sex-linked differences in immune response and autoimmunity, with environmental factors, sex hormones, and X-chromosome inactivation — the process by which a second X chromosome is silenced — all seen as having roles.
More recently, different groups of researchers have homed in on a long noncoding RNA fragment called X-inactive specific transcript, or Xist, as a potential driver of sex bias in autoimmune disease. Xist, which occurs in female mammals, has been known since the 1990s as the master regulator of X-chromosome inactivation, the process by which the second X chromosome is silenced, averting a fatal double dose of X-linked genes.
The inactivation process, which scientists liken to wrapping the extra X with a fluffy cloud of proteins, occurs early in embryonic development. After its initial work silencing the X, Xist is produced throughout the female’s life, allowing X inactivation to be maintained.
But is it possible that Xist, and the many dozens of proteins it recruits to keep that extra X chromosome silent, can also provoke autoimmunity? This is the question that several teams of researchers have been grappling with, resulting in provocative findings and opening exciting new avenues of discovery.
Xist Protein Complexes Make Male Mice Vulnerable to Lupus
In February, researchers Howard Chang, MD, PhD, and Diana Dou, PhD, of Stanford University in Stanford, California, made worldwide news when they published results from an experiment using male mice genetically engineered to carry a non-silencing form of Xist on one of their chromosomes.
Xist acts like a scaffold, recruiting multiple protein complexes to help it do its job. Dr. Dou explained in an interview that her team has been eyeing suspiciously for years the dozens of proteins Xist recruits in the process of X-chromosome inactivation, many of which are known autoantigens.
When the mice were injected with pristane, a chemical that induces lupus-like autoimmunity in mice, the Xist-producing males developed symptoms at a rate similar to that of females, while wild-type male mice did not.
By using a male model, the scientists could determine whether Xist could cause an increased vulnerability for autoimmunity absent the influence of female hormones and development. “Everything else about the animal is male,” Dr. Dou commented. “You just add the formation of the Xist ribonucleoprotein particles — Xist RNA plus the associating proteins — to male cells that would not ordinarily have these particles. Is just having the particles present in these animals sufficient to increase their autoimmunity? This is what our paper showed: That just having expression of Xist, the presence of these Xist [ribonucleoproteins], is enough in permissive genetic backgrounds to invoke higher incidence and severity of autoimmune disease development in our pristane-induced lupus model.”
The Stanford group sees the Xist protein complex, which they have studied extensively, as a key to understanding how Xist might provoke autoimmunity. Nonetheless, Dr. Dou said, “It’s important to note that there are other contributing factors, which is why not all females develop autoimmunity, and we had very different results in our autoimmune-resistant mouse strain compared to the more autoimmune-prone strain. Xist is a factor, but many factors are required to subvert the checkpoints in immune balance and allow the progression to full-blown autoimmunity.”
Faulty X Inactivation and Gene Escape
The understanding that Xist might be implicated in autoimmune disease — and explain some of its female bias — is not new.
About a decade ago, Montserrat Anguera, PhD, a biologist at the University of Pennsylvania, Philadelphia, began looking at the relationship of X-chromosome inactivation, which by definition involves Xist, and lupus.
Dr. Anguera hypothesized that imperfect X inactivation allowed for greater escape of genes associated with immunity and autoimmunity. Studying patients with lupus, Dr. Anguera found that the silencing process was abnormal, allowing more of these genes to escape the silenced X — including toll-like receptor 7 (TLR-7) and other genes implicated in the pathogenesis of lupus.
“If you get increased expression of certain genes from the [silenced] X, like TLR-7, it can result in autoimmune disease,” Dr. Anguera said. “So what we think is that in the lupus patients, because the silencing is impacted, you’re going to have more expression happening from the inactive X. And then in conjunction with the active X, that’s going to throw off the dosage [of autoimmunity-linked genes]. You’re changing the dosage of genes, and that’s what’s critical.”
Even among patients with lupus whose symptoms are well controlled with medication, “if you look at their T cells and B cells, they still have messed up X inactivation,” Dr. Anguera said. “The Xist RNA that’s supposed to be tethered to the inactive X in a fluffy cloud is not localized, and instead is dispersed all over the nucleus.”
Dr. Anguera pointed out that autoimmune diseases are complex and can result from a combination of factors. “You also have a host of hormonal and environmental contributors, such as previous viral infections,” she said. And of course men can also develop lupus, meaning that the X chromosome cannot explain everything.
Dr. Anguera said that, while the findings by the Stanford scientists do not explain the full pathogenesis of lupus and related diseases, they still support a strong role for Xist in sex-biased autoimmune diseases. “It’s sort of another take on it,” she said.
Is It the Proteins, the RNA, or Both?
The Stanford team points to the proteins recruited by Xist in the process of X-chromosome inactivation as the likely trigger of autoimmunity. However, a group of researchers at Johns Hopkins University in Baltimore, Maryland, made the case in a 2022 paper that Xist RNA itself was dangerous. They found that numerous short RNA sequences within the Xist molecule serve as ligands for TLR-7. And TLR-7 ligation causes plasmacytoid dendritic cells to overproduce type 1 interferon, a classic hallmark of lupus.
“Within rheumatology, the diseases that tend to be most female biased are the ones that are antibody positive and have this presence of upregulated interferon,” explained Brendan Antiochos, MD. “Lupus is an example of that. Sjögren’s syndrome is another. So there’s always been this quest to want to understand the mechanisms that explain why women would have more autoimmunity. And are there specific pathways which could contribute? One of the key pathways that’s been shown in humans and in mice to be important in lupus is toll-like receptor signaling.” Most convincingly, one recent study showed that people who have a gain-of-function mutation in their TLR-7 gene get a spontaneous form of lupus.
These findings led Erika Darrah, PhD, and her colleague Dr. Antiochos to begin looking more deeply into which RNAs could be triggering this signaling pathway. “We started to think: Well, there is this sex bias. Could it be that women have unique RNAs that could potentially act as triggers for TLR-7 signaling?” Dr. Darrah said.
Dr. Darrah and Dr. Antiochos looked at publicly available genetic data to identify sex-biased sources of self-RNA containing TLR-7 ligands. Xist, they found, was chock full of them. “Every time we analyzed that data, no matter what filter we applied, Xist kept popping out over and over again as the most highly female skewed RNA, the RNA most likely to contain these TLR-7 binding motifs,” Dr. Darrah said. “We started to formulate the hypothesis that Xist was actually promoting responses that were dangerous and pathogenic in lupus.”
That finding led the team to conduct in-vitro experiments that showed different fragments of Xist can activate TLR-7, resulting in higher interferon production. Finally, they looked at blood and kidney cells from women with lupus and found that higher Xist expression correlated with more interferon production, and higher disease activity. “The more Xist, the sicker people were,” Dr. Darrah said.
Xist’s Other Functions
Xist was first studied in the 1990s, and most research has centered on its primary role in X-chromosome inactivation. A research group led by Kathrin Plath, PhD, at the University of California, Los Angeles, has been occupied for years with untangling exactly how Xist does what it does. “It’s a very clever RNA, right? It can silence the whole chromosome,” Dr. Plath said in an interview.
In 2021, Dr. Plath and her colleagues established in detail how Xist executes silencing, setting down pairs of molecules in specific spots along the chromosome and building huge protein clouds around them. “We worked on learning where Xist binds and what proteins it binds, drilling down to understand how these proteins and the RNA are coming together.”
Dr. Plath has long suspected that Xist has other functions besides X inactivation, and she and her colleagues are starting to identify them. Early this year they published the surprising finding that Xist can regulate gene expression in autosomes, or non–sex-linked chromosomes, “which it might well also do in cancer cells and lymphocytes,” Dr. Plath said. “And now there is this new evidence of an autoimmune function,” she said. “It’s a super exciting time.”
The different hypotheses surrounding Xist’s role in sex-biased autoimmunity aren’t mutually exclusive, Dr. Plath said. “There’s a tremendous enrichment of proteins occurring” during X inactivation, she said, supporting the Stanford team’s hypothesis that proteins are triggering autoimmunity. As for the Johns Hopkins researchers’ understanding that Xist RNA itself is the trigger, “I’m totally open to that,” she said. “Why can’t it be an autoantigen?”
The other model in the field, Dr. Plath noted, is the one proposed by Dr. Anguera — “that there’s [gene] escape from X-inactivation — that females have more escape expression, and that Xist is more dispersed in the lymphocytes [of patients with lupus]. In fact, Xist becoming a little dispersed might make it a better antigen. So I do think everything is possible.”
The plethora of new findings related to autoimmunity has caused Dr. Plath to consider redirecting her lab’s focus toward more translational work, “because we are obviously good at studying Xist.” Among the mysteries Dr. Plath would like to solve is how some genes manage to escape the Xist cloud.
What is needed, she said, is collaboration. “Everyone will come up with different ideas. So I think it’s good to have more people look at things together. Then the field will achieve a breakthrough treatment.”
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<root generator="drupal.xsl" gversion="1.7"> <header> <fileName>167534</fileName> <TBEID>0C04F5BD.SIG</TBEID> <TBUniqueIdentifier>MD_0C04F5BD</TBUniqueIdentifier> <newsOrJournal>News</newsOrJournal> <publisherName>Frontline Medical Communications</publisherName> <storyname/> <articleType>2</articleType> <TBLocation>QC Done-All Pubs</TBLocation> <QCDate>20240402T153106</QCDate> <firstPublished>20240402T153332</firstPublished> <LastPublished>20240402T153332</LastPublished> <pubStatus qcode="stat:"/> <embargoDate/> <killDate/> <CMSDate>20240402T153332</CMSDate> <articleSource/> <facebookInfo/> <meetingNumber/> <byline>Jennie Smith</byline> <bylineText>JENNIE SMITH</bylineText> <bylineFull>JENNIE SMITH</bylineFull> <bylineTitleText>MDedge News</bylineTitleText> <USOrGlobal/> <wireDocType/> <newsDocType>Feature</newsDocType> <journalDocType/> <linkLabel/> <pageRange/> <citation/> <quizID/> <indexIssueDate/> <itemClass qcode="ninat:text"/> <provider qcode="provider:imng"> <name>IMNG Medical Media</name> <rightsInfo> <copyrightHolder> <name>Frontline Medical News</name> </copyrightHolder> <copyrightNotice>Copyright (c) 2015 Frontline Medical News, a Frontline Medical Communications Inc. company. All rights reserved. This material may not be published, broadcast, copied, or otherwise reproduced or distributed without the prior written permission of Frontline Medical Communications Inc.</copyrightNotice> </rightsInfo> </provider> <abstract/> <metaDescription>Female bias in autoimmune disease can be profound, with nine females developing lupus for every male affected, and nearly twice that ratio seen in Sjögren disea</metaDescription> <articlePDF/> <teaserImage>300967</teaserImage> <teaser>Researchers are homing in on a long non-coding RNA, essential to X chromosome inactivation, as the culprit in sex-biased autoimmune diseases like lupus. While there are different theories as to how Xist causes harm, and much left to be learned, the findings offer hope for new treatment targets and approaches.</teaser> <title>Autoimmunity’s Female Bias and the Mysteries of Xist</title> <deck/> <disclaimer/> <AuthorList/> <articleURL/> <doi/> <pubMedID/> <publishXMLStatus/> <publishXMLVersion>1</publishXMLVersion> <useEISSN>0</useEISSN> <urgency/> <pubPubdateYear/> <pubPubdateMonth/> <pubPubdateDay/> <pubVolume/> <pubNumber/> <wireChannels/> <primaryCMSID/> <CMSIDs/> <keywords/> <seeAlsos/> <publications_g> <publicationData> <publicationCode>rn</publicationCode> <pubIssueName/> <pubArticleType/> <pubTopics/> <pubCategories/> <pubSections/> </publicationData> <publicationData> <publicationCode>pn</publicationCode> <pubIssueName/> <pubArticleType/> <pubTopics/> <pubCategories/> <pubSections/> </publicationData> <publicationData> <publicationCode>nr</publicationCode> <pubIssueName/> <pubArticleType/> <pubTopics/> <pubCategories/> <pubSections/> <journalTitle>Neurology Reviews</journalTitle> <journalFullTitle>Neurology Reviews</journalFullTitle> <copyrightStatement>2018 Frontline Medical Communications Inc.,</copyrightStatement> </publicationData> <publicationData> <publicationCode>im</publicationCode> <pubIssueName/> <pubArticleType/> <pubTopics/> <pubCategories/> <pubSections/> </publicationData> <publicationData> <publicationCode>fp</publicationCode> <pubIssueName/> <pubArticleType/> <pubTopics/> <pubCategories/> <pubSections/> </publicationData> <publicationData> <publicationCode>skin</publicationCode> <pubIssueName/> <pubArticleType/> <pubTopics/> <pubCategories/> <pubSections/> </publicationData> </publications_g> <publications> <term canonical="true">26</term> <term>25</term> <term>22</term> <term>21</term> <term>15</term> <term>13</term> </publications> <sections> <term canonical="true">27980</term> <term>39313</term> </sections> <topics> <term canonical="true">241</term> <term>289</term> <term>285</term> <term>251</term> <term>290</term> <term>322</term> <term>231</term> <term>29134</term> </topics> <links> <link> <itemClass qcode="ninat:picture"/> <altRep contenttype="image/jpeg">images/240127c7.jpg</altRep> <description role="drol:caption">Dr. Diana Dou</description> <description role="drol:credit"/> </link> <link> <itemClass qcode="ninat:picture"/> <altRep contenttype="image/jpeg">images/240127c9.jpg</altRep> <description role="drol:caption">Dr. Montserrat Anguera</description> <description role="drol:credit">University of Pennsylvania</description> </link> <link> <itemClass qcode="ninat:picture"/> <altRep contenttype="image/jpeg">images/240127c5.jpg</altRep> <description role="drol:caption">Johns Hopkins University researchers studying Xist (left to right): Daniela Trejo-Zambrano, Jonathan Crawford, Erika Darrah, Brendan Antiochos, Hong Wang</description> <description role="drol:credit">Alexander Girgis</description> </link> <link> <itemClass qcode="ninat:picture"/> <altRep contenttype="image/jpeg">images/240127c6.jpg</altRep> <description role="drol:caption">Dr. Erika Darrah</description> <description role="drol:credit">Wes Linda</description> </link> <link> <itemClass qcode="ninat:picture"/> <altRep contenttype="image/jpeg">images/240127c8.jpg</altRep> <description role="drol:caption">Dr. Kathrin Plath</description> <description role="drol:credit"/> </link> </links> </header> <itemSet> <newsItem> <itemMeta> <itemRole>Main</itemRole> <itemClass>text</itemClass> <title>Autoimmunity’s Female Bias and the Mysteries of Xist</title> <deck/> </itemMeta> <itemContent> <p>Female bias in autoimmune disease can be profound, with nine females developing lupus for every male affected, and nearly twice that ratio seen in Sjögren disease. </p> <p>For years, researchers have worked to determine the reasons for sex-linked differences in immune response and autoimmunity, with environmental factors, sex hormones, and X-chromosome inactivation — the process by which a second X chromosome is silenced — all seen as having roles.<br/><br/>More recently, different groups of researchers have homed in on a long noncoding RNA fragment called X-inactive specific transcript, or Xist, as a potential driver of sex bias in autoimmune disease. Xist, which occurs in female mammals, has been known since the 1990s as the master regulator of X-chromosome inactivation, the process by which the second X chromosome is silenced, averting a fatal double dose of X-linked genes. <br/><br/>The inactivation process, which scientists liken to wrapping the extra X with a fluffy cloud of proteins, occurs early in embryonic development. After its initial work silencing the X, Xist is produced throughout the female’s life, allowing X inactivation to be maintained. <br/><br/>But is it possible that Xist, and the many dozens of proteins it recruits to keep that extra X chromosome silent, can also provoke autoimmunity? This is the question that several teams of researchers have been grappling with, resulting in provocative findings and opening exciting new avenues of discovery. <br/><br/></p> <h2>Xist Protein Complexes Make Male Mice Vulnerable to Lupus</h2> <p>In February, researchers <span class="Hyperlink"><a href="https://profiles.stanford.edu/howard-chang?tab=teaching">Howard Chang, MD, PhD</a></span>, and <span class="Hyperlink"><a href="https://profiles.stanford.edu/diana-dou">Diana Dou, PhD</a></span>, of Stanford University in Stanford, California, made worldwide news when they <span class="Hyperlink"><a href="https://www.cell.com/cell/fulltext/S0092-8674(24)00002-3">published results</a></span> from an experiment using male mice genetically engineered to carry a non-silencing form of Xist on one of their chromosomes.</p> <p>[[{"fid":"300967","view_mode":"medstat_image_flush_left","fields":{"format":"medstat_image_flush_left","field_file_image_alt_text[und][0][value]":"Dr. Diana Dou of Stanford University in Stanford, California","field_file_image_credit[und][0][value]":"","field_file_image_caption[und][0][value]":"Dr. Diana Dou"},"type":"media","attributes":{"class":"media-element file-medstat_image_flush_left"}}]]Xist acts like a scaffold, recruiting multiple protein complexes to help it do its job. Dr. Dou explained in an interview that her team has been eyeing suspiciously for years the dozens of proteins Xist recruits in the process of X-chromosome inactivation, many of which are known autoantigens.<br/><br/>When the mice were injected with pristane, a chemical that induces lupus-like autoimmunity in mice, the Xist-producing males developed symptoms at a rate similar to that of females, while wild-type male mice did not.<br/><br/>By using a male model, the scientists could determine whether Xist could cause an increased vulnerability for autoimmunity absent the influence of female hormones and development. “Everything else about the animal is male,” Dr. Dou commented. “You just add the formation of the Xist ribonucleoprotein particles — Xist RNA plus the associating proteins — to male cells that would not ordinarily have these particles. Is just having the particles present in these animals sufficient to increase their autoimmunity? This is what our paper showed: That just having expression of Xist, the presence of these Xist [ribonucleoproteins], is enough in permissive genetic backgrounds to invoke higher incidence and severity of autoimmune disease development in our pristane-induced lupus model.”<br/><br/>The Stanford group sees the Xist protein complex, which they have <span class="Hyperlink"><a href="https://www.nature.com/articles/s41467-020-20040-3">studied extensively</a></span>, as a key to understanding how Xist might provoke autoimmunity. Nonetheless, Dr. Dou said, “It’s important to note that there are other contributing factors, which is why not all females develop autoimmunity, and we had very different results in our autoimmune-resistant mouse strain compared to the more autoimmune-prone strain. Xist is a factor, but many factors are required to subvert the checkpoints in immune balance and allow the progression to full-blown autoimmunity.”<br/><br/></p> <h2>Faulty X Inactivation and Gene Escape </h2> <p>The understanding that Xist might be implicated in autoimmune disease — and explain some of its female bias — is not new. </p> <p>About a decade ago, <span class="Hyperlink"><a href="https://www.vet.upenn.edu/people/faculty-clinician-search/MONTSERRATANGUERA">Montserrat Anguera, PhD</a></span>, a biologist at the University of Pennsylvania, Philadelphia, began looking at the relationship of X-chromosome inactivation, which by definition involves Xist, and lupus. <br/><br/>[[{"fid":"300970","view_mode":"medstat_image_flush_right","fields":{"format":"medstat_image_flush_right","field_file_image_alt_text[und][0][value]":"Dr. Montserrat Anguera, a biologist at the University of Pennsylvania, Philadelphia","field_file_image_credit[und][0][value]":"University of Pennsylvania","field_file_image_caption[und][0][value]":"Dr. Montserrat Anguera"},"type":"media","attributes":{"class":"media-element file-medstat_image_flush_right"}}]]Dr. Anguera hypothesized that imperfect X inactivation allowed for greater escape of genes associated with immunity and autoimmunity. Studying patients with lupus, Dr. Anguera found that the <span class="Hyperlink"><a href="https://www.pnas.org/doi/full/10.1073/pnas.2024624118">silencing process was abnormal</a></span>, allowing more of these genes to escape the silenced X — including toll-like receptor 7 (TLR-7) and other genes implicated in the pathogenesis of lupus.<br/><br/>“If you get increased expression of certain genes from the [silenced] X, like TLR-7, it can result in autoimmune disease,” Dr. Anguera said. “So what we think is that in the lupus patients, because the silencing is impacted, you’re going to have more expression happening from the inactive X. And then in conjunction with the active X, that’s going to throw off the dosage [of autoimmunity-linked genes]. You’re changing the dosage of genes, and that’s what’s critical.”<br/><br/>Even among patients with lupus whose symptoms are well controlled with medication, “if you look at their T cells and B cells, they still have messed up X inactivation,” Dr. Anguera said. “The Xist RNA that’s supposed to be tethered to the inactive X in a fluffy cloud is not localized, and instead is dispersed all over the nucleus.”<br/><br/>Dr. Anguera pointed out that autoimmune diseases are complex and can result from a combination of factors. “You also have a host of hormonal and environmental contributors, such as previous viral infections,” she said. And of course men can also develop lupus, meaning that the X chromosome cannot explain everything. <br/><br/>Dr. Anguera said that, while the findings by the Stanford scientists do not explain the full pathogenesis of lupus and related diseases, they still support a strong role for Xist in sex-biased autoimmune diseases. “It’s sort of another take on it,” she said.<br/><br/></p> <h2>Is It the Proteins, the RNA, or Both? </h2> <p>The Stanford team points to the proteins recruited by Xist in the process of X-chromosome inactivation as the likely trigger of autoimmunity. However, a group of researchers at Johns Hopkins University in Baltimore, Maryland, made the case in a <span class="Hyperlink"><a href="https://journals.aai.org/jimmunol/article/208/1_Supplement/108.02/236370/XIST-is-a-source-of-TLR7-ligands-underlying-the">2022 paper</a></span> that Xist RNA itself was dangerous. They found that numerous short RNA sequences within the Xist molecule serve as ligands for TLR-7. And TLR-7 ligation causes plasmacytoid dendritic cells to overproduce type 1 interferon, a classic hallmark of lupus.</p> <p>[[{"fid":"300968","view_mode":"medstat_image_flush_left","fields":{"format":"medstat_image_flush_left","field_file_image_alt_text[und][0][value]":"Johns Hopkins University researchers studying Xist (left to right): Daniela Trejo-Zambrano, Jonathan Crawford, Erika Darrah, Brendan Antiochos, Hong Wang.","field_file_image_credit[und][0][value]":"Alexander Girgis","field_file_image_caption[und][0][value]":"Johns Hopkins University researchers studying Xist (left to right): Daniela Trejo-Zambrano, Jonathan Crawford, Erika Darrah, Brendan Antiochos, Hong Wang"},"type":"media","attributes":{"class":"media-element file-medstat_image_flush_left"}}]]“Within rheumatology, the diseases that tend to be most female biased are the ones that are antibody positive and have this presence of upregulated interferon,” explained <span class="Hyperlink"><a href="https://www.hopkinsmedicine.org/profiles/details/brendan-antiochos">Brendan Antiochos, MD</a></span>. “Lupus is an example of that. Sjögren’s syndrome is another. So there’s always been this quest to want to understand the mechanisms that explain why women would have more autoimmunity. And are there specific pathways which could contribute? One of the key pathways that’s been shown in humans and in mice to be important in lupus is toll-like receptor signaling.” Most convincingly, <span class="Hyperlink"><a href="https://www.nature.com/articles/s41586-022-04642-z">one recent study</a></span> <span class="Hyperlink">showed</span> that people who have a gain-of-function mutation in their TLR-7 gene get a spontaneous form of lupus. <br/><br/>[[{"fid":"300966","view_mode":"medstat_image_flush_left","fields":{"format":"medstat_image_flush_left","field_file_image_alt_text[und][0][value]":"Dr. Erika Darrah, Assistant Professor in the Division of Rheumatology at Johns Hopkins University, Baltimore, Maryland","field_file_image_credit[und][0][value]":"Wes Linda","field_file_image_caption[und][0][value]":"Dr. Erika Darrah"},"type":"media","attributes":{"class":"media-element file-medstat_image_flush_left"}}]]These findings led <span class="Hyperlink"><a href="https://gradimmunology.med.som.jhmi.edu/darrah/">Erika Darrah, PhD</a></span>, and her colleague Dr. Antiochos to begin looking more deeply into which RNAs could be triggering this signaling pathway. “We started to think: Well, there is this sex bias. Could it be that women have unique RNAs that could potentially act as triggers for TLR-7 signaling?” Dr. Darrah said. <br/><br/>Dr. Darrah and Dr. Antiochos looked at publicly available genetic data to identify sex-biased sources of self-RNA containing TLR-7 ligands.<span class="apple-converted-space"> Xist, they found, was chock full of them. “</span>Every time we analyzed that data, no matter what filter we applied, Xist kept popping out over and over again as the most highly female skewed RNA, the RNA most likely to contain these TLR-7 binding motifs,” Dr. Darrah said. “We started to formulate the hypothesis that Xist was actually promoting responses that were dangerous and pathogenic in lupus.” <br/><br/>That finding led the team to conduct in-vitro experiments that showed different fragments of Xist can activate TLR-7, resulting in higher interferon production. Finally, they looked at blood and kidney cells from women with lupus and found that higher Xist expression correlated with more interferon production, and higher disease activity. “The more Xist, the sicker people were,” Dr. Darrah said. <br/><br/></p> <h2>Xist’s Other Functions</h2> <p>Xist was first studied in the 1990s, and most research has centered on its primary role in X-chromosome inactivation. A research group led by <span class="Hyperlink"><a href="https://www.biolchem.ucla.edu/people/kathrin-plath/">Kathrin Plath, PhD</a></span>, at the University of California, Los Angeles, has been occupied for years with untangling exactly how Xist does what it does. “It’s a very clever RNA, right? It can silence the whole chromosome,” Dr. Plath said in an interview. </p> <p>[[{"fid":"300969","view_mode":"medstat_image_flush_right","fields":{"format":"medstat_image_flush_right","field_file_image_alt_text[und][0][value]":"Dr. Kathrin Plath of the University of California, Los Angeles","field_file_image_credit[und][0][value]":"","field_file_image_caption[und][0][value]":"Dr. Kathrin Plath"},"type":"media","attributes":{"class":"media-element file-medstat_image_flush_right"}}]]In 2021, Dr. Plath and her colleagues established in detail <span class="Hyperlink"><a href="https://www.cell.com/cell/fulltext/S0092-8674(21)01275-7">how Xist executes silencing</a></span>, setting down pairs of molecules in specific spots along the chromosome and building huge protein clouds around them. “We worked on learning where Xist binds and what proteins it binds, drilling down to understand how these proteins and the RNA are coming together.”<br/><br/>Dr. Plath has long suspected that Xist has other functions besides X inactivation, and she and her colleagues are starting to identify them. Early this year they published the surprising finding that Xist can <span class="Hyperlink"><a href="https://www.cell.com/cell/fulltext/S0092-8674(23)01319-3">regulate gene expression in autosomes</a></span>, or non–sex-linked chromosomes, “which it might well also do in cancer cells and lymphocytes,” Dr. Plath said. “And now there is this new evidence of an autoimmune function,” she said. “It’s a super exciting time.”<br/><br/>The different hypotheses surrounding Xist’s role in sex-biased autoimmunity aren’t mutually exclusive, Dr. Plath said. “There’s a tremendous enrichment of proteins occurring” during X inactivation, she said, supporting the Stanford team’s hypothesis that proteins are triggering autoimmunity. As for the Johns Hopkins researchers’ understanding that Xist RNA itself is the trigger, “I’m totally open to that,” she said. “Why can’t it be an autoantigen?”<br/><br/>The other model in the field, Dr. Plath noted, is the one proposed by Dr. Anguera — “that there’s [gene] escape from X-inactivation — that females have more escape expression, and that Xist is more dispersed in the lymphocytes [of patients with lupus]. In fact, Xist becoming a little dispersed might make it a better antigen. So I do think everything is possible.”<br/><br/>The plethora of new findings related to autoimmunity has caused Dr. Plath to consider redirecting her lab’s focus toward more translational work, “because we are obviously good at studying Xist.” Among the mysteries Dr. Plath would like to solve is how some genes manage to escape the Xist cloud. <br/><br/>What is needed, she said, is collaboration. “Everyone will come up with different ideas. So I think it’s good to have more people look at things together. Then the field will achieve a breakthrough treatment.”<span class="end"/></p> </itemContent> </newsItem> <newsItem> <itemMeta> <itemRole>teaser</itemRole> <itemClass>text</itemClass> <title/> <deck/> </itemMeta> <itemContent> </itemContent> </newsItem> </itemSet></root>
